Cellular uptake of taurine by lactating porcine mammary tissue

Milk taurine plays a critical role in neonatal development. Taurine uptake in lactating sow mammary tissue has not been characterized previously. The kinetic properties, ion dependence and substrate specificity of taurine upt ake were characterized in mammary tissue collected from lactating sows at s laughter. Tissue explants were incubated in an isosmotic physiologic buffer with [H-3]taurine tracer to measure taurine uptake. Taurine uptake was dep endent upon the presence of extracellular sodium and chloride ions, which i s consistent with the co-transport of sodium and chloride with taurine. Upt ake was not dependent upon ion exchange mechanisms or upon furosemide-sensi tive ion co-transport. Taurine uptake was saturable and exhibited an appare nt K-m of 20 muM and a V-max of 386 mu mol/kg cell water/30 min. Substrate specificity studies indicated a strong interaction of beta -amino acids wit h the taurine transport system. Taurine transport in lactating sow mammary tissue is therefore a high affinity, sodium-dependent mechanism specific fo r beta -amino acids, and is analogous to sodium-dependent taurine uptake in other tissues. The high affinity and high specificity of the taurine uptak e system allows for concentration of taurine within the mammary cell and is ultimately responsible for provision of taurine required for neonatal deve lopment. (C) 2001 Elsevier Science Inc. All rights reserved.